Abstract

Synchrotron-radiation glancing-incidence and angle-resolved photoelectron spectroscopy (PES) is used to study the oxides grown in air on a single-crystal Nb(100) surface. Both core-level and valance-band PES are measured for various heat treatments. Glancing-incidence excitation was used to characterize the outer layer without influence from the substrate and to profile through various oxides by varying the incidence angle. Immediately adjacent to this amorphous layer is a layer of , which contributes to the density of states at below the Fermi level. Thereafter, there exist other oxides that interface with the metal substrate. Annealing at induces a “mild” chemical reaction, which is contained essentially in the oxide layer. Annealing at causes oxygen diffusion into the metal and leaves an oxide layer consisting primarily of and a roughened surface, as evidenced by angle-resolved photoemission measurements. Oxide composition alteration caused by annealing at these moderated temperatures is believed to be interface mediated.